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When I read the dimension table, it appears that the belly section diameter is around 150 mm. This is way more than normal. I'd say somewhere between 90 and 110 mm seems more appropriate for a 185 cc single. In AG Bells book, the belly should be around 2.5 times header diameter, max. That would be the header diameter next to the port if using a tapered header.

The 60's and 70's design formulas like Bells have been left behind a long time ago. Much larger belly diameters are common now as is bigger stingers and stinger length considerations.

Yeah I didn't think 150mm looked super large, I still have to try other software and fix up some numbers, maybe it will get closer to 2.5x header diameter, but I would rather go off the dimensions that are calculated rather than guess.

Jan Theil and Frits Overmars are both pretty active on Facebook.

They are both posting quite often in the "2 stroke research & development" group, and would likely be glad to answer your questions directly.

I would love to talk to them, but I am quite anti-facebook.

I will have to try a few other softwares and see what they spit out. The blair formula made the belly like 80mm, I could hardly tell where the cones started and ended. Header diameter is like 40mm.

How do you modify the pipe to go to a ~100mm belly? just guess and taper the cones more, but keep the lengths roughly the same, or keep the tapers and extend the belly or shorten the pipe?

Ok, so I definitely want to raise and widen the port? I want to keep it able to run on the stock pipe because I don't have the means to build this right now. I think that will limit how high I can make the exhaust port. I also just don't expect an extreme amount of power out of this bike, credit where its due, its not bad for what it is. If BMEP hits 6 that is probably pretty good.

As for the blowdown... I'll believe you that its short, I think I saw 20deg was good for a chainsaw lol. This early model engine has only one transfer per side. I'm assuming widening the transfers and exhaust both improve blowdown time-area because it should speed up flow out and in? We are aiming for a higher pressure differential of the incoming air and outgoing air, so even things like a bigger carb or more aggressive intake timing help, right?

I plan on bending this entire pipe out in a brake because I dont have a roller, it will be simplified, header will be mostly parallel and I want to keep as much of the diffuser out of the main bend as possible, then I can cover more ground bending a longer cone.

73 ts185 with light porting. I know the factory pipe is supposed to be "good", but with the factory ports I can tell the flow is reverting, the transfers are very dark. I calculated the blowdown area to be 21deg, so I think that is ample with a good pipe, I think the stock pipe is actually just very restrictive... It should be since it is also a muffler. I'm just going to chamfer the exhaust and that will raise it just a hair to further increase blowdown, so I began designing a pipe since that is the main issue I think.

I am just using a free software for now, Ezin Hobeki's Pipe designer. Using the Fritz Overmars formula gives a pretty reasonable pipe, Blair was pretty much just spitting out a straight pipe. One thing I am not really sure of is how does it know the width of the exhaust flange? D0 is a few mm too large to connect to the cylinder. Are you just expected to neck up or port match? And should the exhaust port with be measured by arc length or chord length? I am using arc length because I transferred the port to masking tape, but I am assuming it is just asking for the linear width across the port, I did not have anything small enough to measure it with though. I am open to any other pointers as well, this is my first time doing this, just running the numbers though.

Heh, I am pretty pleased with my stock carb. Some non adjustable Keihin feedback carb that I devacuumed and converted to a manual secondary. Keeps me in the STS autocross class with your average modified NA Miata and runs right along with them. Only thing keeping me from slapping the bike carbs on, along with the suspension upgrades needed to handle the speed, is it will bump me up to SMF, which also includes new Civic Type Rs. The carbs will easily bump it up to around 180hp with a lot of low end and the top end being limited to how much rpm it can take without causing piston slap. Either way, its not something you would even expect to be quick.

It is an 87 Honda Accord, 2.0l. Ive got the carbs and can just as easily mount these as I could make a manifold for DCOEs. I believe they are Mikuni VM29s, push/pull round slides. I have it written down in a notebook, so I am not 100% sure, just going off this jetsrus page https://jetsrus.com/carburetor/carb_mikuni_VM29_carb_exploded_view_parts.html Kind of funny, its a very similar carb to what I was just asking about, just made for a 4 cylinder 4 stroke.

yeah you should be able to sort it. a good portion of my bikes are that old, and i'm running even smaller carbs on a few, they always need some dressing of the body. (polish the inside where the slide goes)

ive never seen an fcr on a 2 stroke but anything can be made to work I would guess. heck my 2023 honda xr150 is carbureted and it doesn't even have a push pull carb on it (which surprised me, I thought they were mandated at one point?).

another option is an aftermarket 'nibbi' brand carburetor. not push pull but the quality is actually excellent, even though they are dirt, dirt, like suspiciously dirt cheap.  Yes, i have one and  was shocked how good a 40 dollar carb was.

Yeah, I hit it with a scotch brite pad once, its going to need to be cleaned up better than that. I'll save my 40 bucks though unless I screw it up somehow lol.

Ok, idk if I will go the fcr route, I really like them though, just nice to confirm they should work. Ive never seen one used on a 2 stroke either. And yeah, that is really odd, I thought it was mandated too, thats not even a model that was grandfathered into the current year.

Question? If you are building a flat tracker why do you want such small 22mm carbs? Anyway a VM round slide is a great choice , when modified wit a  UFO a round slide will out flow a flat slide up to 15/16 throttle. And if its bored out most of the slide eddy will be eliminatd for even better flow, also the air bleed bosses can be stream lined at the opening in the rear. In the end you have a awesome sleeper carb. And I can fabricate venturi divider in either round or flat slide carbs , that make for a much more linear power delivery. You can give me a call if you like and we can talk. Check out my web site 

Richstaylordporting.com

702-858-9177

Oh I'm not building one with a 22mm carb. That is what is on my TS185. At the smallest itd be what comes stock on a banshee. The smallest fcr Id use is a 32mm, but that'd probably be down to availability/appropriate size. I'm definitely not looking for tons of power, I'm sure it will have plenty on tap. If I were to get rz350 carbs I might look into modding them to get them dialed in better, but the fcr is probably flexible enough as it is. I'm actually looking into putting some round slides on my car, I might actually call you up about that instead lol.

Oh I see that. I think I looked at them, but didn't notice they were any different. Decent option.

Any thoughts on the FCR though?

if your vm22 is hanging up, either the carb is slap worn out , the cable is fucked or something else.

Well it is 50 years old. Its a bit odd, doesn't get ridden much, just happened out of the blue. I need to blue the slide and see where it is rubbing, may just be able to replace or adjust the aligning peg. Not really worried about that bike though, I was just looking at 2 stroke carbs and wondering why so few were push/pull.

This isn't for any particular application, but I'd like to build a dirt flat tracker style bike with something like a banshee motor in it. Ive got an old 2 stroke now, its got a Mikuni VM22, I know its a good carb, but this one likes to get stuck wide open lately. I'd love a push/pull type throttle, so that really can't even be an issue.

I started looking at later model carbs, such as the Mikuni TM style flat slide, and Mikuni did have a push/pull throttle on some of them, but I don't think that was for the 2 stroke variants. I've heard decent things about the TM, and the 2 stroke models are about as simple as the old VM, the one complaint is when compared to a Keihin FCR (obviously on 4 stroke applications) they are not as easy to get parts for. Others I have seen are pretty exotic like off an RZ500 or NSR250.

But I also got to thinking... What about the Keihin FCR? I think you can get them down to 32mm. Probably disable the accelerator pump if applicable. They can probably be jetted for anything under the sun too. I think they would be a bit big for a lot of applications, but high comp/big bores could get away with it. Anything that would stop me from using one? Any other carb that's relatively easy to come by that I missed?